The present invention relates to a switchable planar high frequency resonator with a superconductor microstructure mounted on a substrate, whose geometry determines its resonance properties, especially the position and width of the resonance, and also relates to a high frequency filter based on it. A switchable high frequency resonator is already known from WO 93/00720. In this reference a resonator is described comprising a microstructure made from a high temperature superconductor on a substrate, over which a gallium arsenide platelet or lamina was glued. The conductivity of the gallium arsenide could be increased by several orders of magnitude by light irradiation. The effective dielectric function of the surroundings of the resonator can be changed which changes the resonance properties of the resonator. When the eigenfrequencies of the resonator are outside of the occurring high frequency spectrum or strongly damped, a filtration is avoided with this resonator.
A tunable bandpass filter is provided with microconductor strip construction methods as described in WO 94/28592. Several resonators made from a high temperature superconductor are mounted together with input and output leads on a complex many layer substrate. This many layer substrate includes a supporting material and a ferroelectric or anti-ferroelectric layer as well as several required buffer layers. An electric field is applied to the ferroelectric or anti-ferroelectric layer which changes the dielectric function of this ferroelectric or anti-ferroelectric layer so that the effective dielectric function of the surroundings is similar changed. By changing the real part of the effective dielectric function, the eigenfrequencies of all resonators in the filter are shifted approximately equally; a filter constructed using this resonator is thus tunable or, in cases in which the tuning region is selected sufficiently wide, also switchable.
An additional method of tuning resonators is described in VDI Research Report, Series 9, p 189 (1994). Perturbing bodies are inserted by mechanical positioning devices in the field over the resonator. A slight change of the effective dielectric function of the surroundings of the strip conductor is achieved by the position change of the perturbing bodies which have constant dielectric properties. This method is more frequently used for compensation or calibration of filter elements, than for dynamic adjustment or for switching.